The invention relates to catalysts and methods for the conversion of carbon dioxide to valuable products. More particularly, the invention relates to carbide catalysts, in particular metal carbide catalysts, for the production of hydrocarbons from carbon dioxide or carbon monoxide.
According to the United States Environmental Protection Agency carbon dioxide is the primary greenhouse gas emitted by humans, accounting for greater than 80% of all greenhouse gases. Therefore, decreasing the emission of carbon dioxide is a priority to reduce and/or avoid the adverse effects of global climate change. One approach to reducing carbon dioxide emissions is electrochemically converting it to fuels and other valuable products. Electrochemical conversion could also provide a method for making renewable biomass fuels (ethanol and biodiesel) and fossil fuels carbon neutral, reducing fossil fuel demand and carbon dioxide emissions. Another option is to transition to renewable energy sources, such as hydro, wind, geothermal, solar, etc. Unfortunately, renewable sources tend to be intermittent and lack portability requiring large scale energy storage to meet energy demands. Conversion of carbon dioxide to fuels could be used with or as an alternative to the energy storage requirements.
A key technological challenge to industrial application of electrochemical conversion of carbon dioxide to useful fuels and other products is the development of catalysts to make the process cost effective. Efficient catalysts enable electrochemical conversions at low overpotential and reasonable current densities. Due to the low reactivity and high stability of carbon dioxide, identification of efficient catalysts to convert carbon dioxide to hydrocarbons has been challenging. For example, copper, a commonly used catalyst for carbon dioxide reduction to hydrocarbons, requires an overpotential on the order of 1 V.
According to the United States Department of Energy, “[t]he major obstacle preventing the efficient conversion of carbon dioxide into energy-bearing products is lack of catalysts” with satisfactory activity at low overpotentials and high electron conversion (US Dept. of Energy, Basic Research Needs: Catalysts for Energy, Report PNNL17712, 2008). Overpotential is related to the loss of energy during the process, so efficient conversion requires low overpotentials. Therefore, it is necessary to find catalytic materials having lower overpotentials to produce hydrocarbons from carbon dioxide more efficiently.